Phonograph pickup having a quadrilateral crystal with only one corner free to flex



April 3, 1951 C. D. ONEAL PHONOGRAPH PICKUP HAVING A QUADRILATERALCRYSTAL WITH ONLY ONE CORNER FREE TO FLEX Filed Nov. 9, 1948 R;JNVENTOR.

Patented Apr. 3, 1951 PHONOGRAPH PICKUP HAVING A QUADRI- LATERAL CRYSTALWITH ONLY ONE CORNER FREE TO FLEX Cieon D. QNeal, Glenside, Pa.,assignor to Philco Corporation, Philadelphia, Pa., a corporation ofPennsylvania Application November 9, 1948, Serial No. 59,168

Claims. 3

The present invention. relates, generally, to transducers of the typeemployed to reproduce sound from phonograph records. More specifically,the invention pertains to piezo-electric crystal pickups adapted,primarily, although not necessarily, for use vith lateral-cut recordswherein the sound track takes the form of a spiral groove which ismodulated laterally in accordance with the recorded sound.

Recent developments in record making techniques have made possible thecommercial production of improved lateral-cut phonograph record discsfor home use, which are characterized by their long playin time,compared with the playing time of present day standard records. Theseimproved records, which have become known to the trade as microgrooverecords, are provided with a lateral-cut modulated groove having anexceedingly fine pitch of approximately 224 to 250 lines per inch, andare capable of being satisfactorily played at a slow turntable speed of33 R. P. M. The combination of this time pitched groove with this slowturntable speed, has made it possible to achieve a sixfold increase inrecording time per disc. In other words, a selection which, for example,normally requires an album of six 12-inch records of the present daystandard type, can now be accommodated on a single l2 inch record of thestated improved type.

However, the provision of an adequate economical reproducer for a recordof the mentioned improved or microgroove type, meets with unusualtechnical and manufacturing problems.

These problems are particularly in evidence when the provision of acrystal pickup for use with such a record is contemplated. Broadly, theproblems involve needle and record wear, and pickuptracking and outputdifiiculties.

The modulated groove of the improved or microgroove record has a widthof the order of .003 of an inch, at the surface of the record. Thegroove is V-cut with a wall angle of about 90 and a bottom radius under.0002 of an inch. In order to obtain satisfactory reproduction with agroove of this size and shape, the needle must have a tip radius of theorder of .001 of an inch. Moreover, because of the fineness of themodulated groove, the material employed in the manufacture of theimproved record must be soft, as compared with the material utilized inthe manufacture of the customary shellac type ecord, if a clean-cut andundistorted modulated groove is to be obtained. In practice, theimproved record is made of suitable plastic material.

The minuteness of the needle, together with the softness of the recordmaterial, necessitates operation of the pickup at an exceedingly lowneedle pressure, so as to prevent unduly rapid wear or the needle andrecord, as well as to achieve a satisfactory signal-to-noise ratio Whilemaintaining an adequate dynamic range. Experimentation has shown thatthe needle pressure should be of the order of 5 grams. This low needlepressure, together with the minuteness of the needle and the smallnessof the modulated groove, gives rise to tracking difiiculties andrequires unusual stability and a high order of compliance in thevibratory mechanical system of the crystal pickup, to prevent the needlefrom jumping out of the groove.

Moreover, because the excursion of modulation is necessarily limited,due to the closeness of grooves, the force available to drive thecrystal is so materially reduced that it becomes a diiiicult matter toobtain a conventional amount of voltage output which can be use directlyfrom the pickup, without a separate and additional stage ofamplification. Also, since response compensation is a process which isaccomplished at the expense of losses in voltage, the provision of agenerating system having a response characteristic which requires nocompensation, entails major problems, especially when the nature of thepickup needle and of the modulated groove tends deleteriously to affectthe output of such a system. The main diniculty arises from the factthat the output voltage produced by the crystal is, in part, a functionof the force with which the crystal is disin response to displacement ofthe needle as it follows the modulated groove. The provision of a systemwhich forcibly displaces the crystal without exerting, against therecord groove, a lateral pressure great enough to mutilate the groove orto cause improper tracking, has been a perpetual source of difiiculties,and these diiiiculties increase as the needle size, the groove width andthe record material hardness decrease.

t is, therefore, the primary object of this invention to overcome theabove stated difficulties and problems and to make possible theeconomical production of a piezoelectric crystal pickup is capable ofeffectively playing records of the mentioned improved or microgroovetype.

Other and more specific objects of the invention have to do withimprovements in the mounting and driving structure for the crystalelement; in the provision of a compact assembly of elements, so as tofacilitate their inclosure in a moistureprooi housing; and in theconstruction relative disposition of parts to insure stability ofcertain parts mechanical compliance other parts, in order to obtain goodreproduction proper tracking and in order to avoid the deleteriouseffects or" mechanical shocks or he like.

The pickup constructed in accordance With the invention includes aneedle having the required minute construction for the properreproduction of the mentioned improved or microgroove records. Thepickup, as a whole, is characterized by its light weight and its abilityto track adequately and to operate effectively, at the desired lowneedle pressure of 5 grams. The invention is especially characterzed bya novel mounting and drivin arrangement for the piezoelectric crystalunit of the pickup. This arrangement is such that, while the lightpressure which is exerted on and by the needle in its side-to-sidecontact with the modulated narrow groove, is insufficient to injure thegroove or to cause mistracking, the force which is developed throughcontact of the groove with the needle, is great enough to produce anoutput voltage at least as high as in conventional apparatus so as toinsure satisfactory reproduction without inclusion of a compensatingnetwork and without the need of a pro-amplifying stage, in thereproducing system.

Other objects and characteristic features, and the manner in which theyare obtained, will be fully understood from the following descriptionbased on the accompanying drawings in which:

Figure l is a perspective view of a piezoelectric crystal unit of thetype employed by this invention;

Figure 2 is an enlarged sectional elevational View of one-half of thepickup cartridge, showing the crystal unit and its associated elementsarranged in accordance with the invention;

Figure 3 is a plan view, on a diiierent scale, of the assembled pickupcartridge with a portion broken away to clarify the showing of certainparts;

Figure 4 is a sectional view through the height of the pickup cartridge,looking in the general direction of arrows 4- 5 of Figure 3; and

Figure 5 is an enlarged perspective view of the pickup cartridge.

Referring more particularly to the drawing, the piezoelectric crystalunit is shown, generally, at it. This unit, as represented in Figure 1,is flat and quadrilateral in shape having four marginal edges Eta, tub,iiic and iiid; defining four corner portions a, h. and (1. However, inactual use, the crystal unit is much smaller than is shown. As used, thecrystal unit measures approximately of an inch square and about as of aninch thick. The crystal unit has all of its surfaces coated. with awaterproofing substance for protection against loss or gain of moisture.In practice, the entire crystal unit, with the exception of its terminalstrips II and i2, conveniently dipped in a suitable rubber solution and,then, is allowed to dry until the teated unit can be handled withoutdanger of unduly removing the coating.

The crystal which the'invention employs, is of the ordinaryRochelle-salt type and of known twister construction including thecustomary electrodes (not shown) with which the terminal strips Ii andi2 are electrically connected. It is known that when a crystal unit ofthe kind above mentioned is used in a phonograph pickup and is afunction of the mechanical force with which the crystal is flex-ed bydisplacement of the needle. Since the needle displacement is governed bythe amplitude of the recorded modulated groove, it will be appreciatedthat when playing a record having a narrow laterally-cut groove withsmall amplitude, such as is the case in the improved or microgrooverecord, the side-to-side displacement of the needle is small, andbecause of the low needle pressure with which it is necessary tooperate, the force acting on the crystal is'likewise small, so that areduction in voltage output follows. In order t remedy this reduction inoutput without additional pre-amplification, it is necessary to increasethe inherent efficiency oi? the crystal unit while operating at reducedmaximum needle excursion and maintaining the desired low needlepressure. This is accomplished, in accordance with the presentinvention, by so mounting the unit that only one corner portion (forexample, corner portion at) of the quadrilateral crystal unit is free toflex, and by associating with said one corner a low inertia vibratorymechanical system particularly devised to drive said one corner with theforce required to produce the desired voltage.

Thus, in accordance with the invention, two adjacent marginal edges, itsand lilo of the quadrilateral crystal unit are reinforced and supportedso as to hold the three corner portions (1, b, and c which are includedin said edges, against motion, and to leave the remaining two adjacentmarginal edges i8?) and iiid and the corner portion at therebetween,free to move. By reinforcing and supporting the crystal unit in themanner mentioned, the stresses to which the unit is subjected bymovement of the mentioned free corner portion, are amplified and, as aresult, the unit is utilized to its fullest extent to produce highvoltage output with slight move ment of said free corner portion.

In the construction illustrated and as is clearly shown in Figures 2 and3 of the drawing, two continuous and right angularly disposed marginaledge portions of the crystal unit, including that edge led from whichthe terminal strips II and i2 extend, are stiffened as by means of arigid frame consisting of right angularly disposed channeled or U-shapedmembers 13 and i l. These members snugly embrace said marginal edgeportions of the crystal unit, and are advantageously fixed in positionby use of a suitable cement applied to the contacting surfaces of saidmembers and crystal unit. At least one channel member 13 is providedwith slots as indicated at I5 and iii (Figure 2) to accommodate theterminal strips ii and i2, respectively.

The crystal unit With its reinforced marginal edge portions is enclosedand supported within a housing indicated, generally, at ll. This housingcompri es complementary half sections is and it of ligh weightnon-conducting material. These sections cooperate to clamp the crystalunit along its reinforced portions. As best seen in Figures 2 and 4, thehousing sections it and l9 are each provided with an inwardly recessedportion 2!! of substantially square configuration. These recessedportions are disposed to confront each other when said half sections areassembled to complete the housing, so that a chamber is provided withinthe housing to accommodate the crystal unit. Also, the housing sections18 and I9 are each provided with a shelf-like portion 2| which boundstwo right angularly disposed sides of the recessed portion of theassociated section. These shelf-like portions are likewise disposed toconfront each other w en the sections of the housing are assembled and,further, are disposed to correspond to the reinforced or stifienedportions of the crystal unit, so as to clamp said portions. Strips 22 ofsuitable cushioning material, such as rubber, are advantageouslyinterposed between said reinforced portions of the crystal unit and saidshelf-like portions of the housing sections to insure retention of theclamped crystal unit and, at the same time, to protect the unit againstundue vibrational shocks.

As shown at 23 in Figures 2 and 3, the housing sections are recessed toprovide a space for accommodating the terminal strips II and I2 and,.2."

as shown at 24 in Figures 2 and 5, said sections are slotted to receivecontact pieces 25 and 26 which are electrically connected to saidstrips, the connection being conveniently obtained by soldering, asindicated at 21 (Figure 2). of each of said contact pieces is exposedoutwardly of the assembled housing, through the associated slot, forengagement with suitable corresponding contact members which areconveniently provided in the customary tone-arm (not shown) to transmitthe voltage from the pickup to the audio stage of the reducing system.The contact pieces 25 and 25 are advantageously located in positionwithin their respective slots by means of a block 28 (Figures 1 and 2)of insulating material, which block fits in said slots and extendsbetween said pieces. As appears in Figures 2, 4 and 5, the housingsections [8 and I 9 are further provided with hollowed-out portionswhich, when said sections are assembled, cooperate to form a generallycircular opening 29 for the purpose presently described.

The above mentioned low inertia vibratory mechanical system, inaccordance with the invention, takes the form of a leverage arrangement,one arm of which is constituted by the needle, the other arm of which isconstituted by a driving chuck in engagement with the free cornerportion d of the crystal unit, and the fulcrum of which is provided byparts of the crystal housing. In practice, the relationship between thelength of the respective lever arms is such that the slight forceexerted at the tip portion of the needle (one lever arm) is amplified atthe crystal-engaging portion of the chuck (other lever arm) so that theforce exerted at the free corner portion of the crystal is great enoughto create, within the crystal, stresses of ample magnitude to producethe desired voltage output. Also in accordance with the invention, thetwo lever arms (the needle and the driving chuck) are associated in sucha manner as to form a reversely bent crank-like leverage assembly, therotational axis A--A (see Figure 2) of which is generally perpendicularto the free edge [0d of the crystal unit and is disposed substantiallymidway between the free corner portion at and the clamped corner portion0 of said edge llld.

As shown in Figure 2, when the pickup cartridge is in operativeposition, with the needle in A part engagement with a record R, thementioned one free edge Hid of the crystal unit becomes located insubstantially confronting relation with respect to the playing surfaceof the record, and the rotational axis AA of the leverage assemblyextends generally in a plane perpendicular to said free edge id of theunit and to said surface of the record. In this manner, the crystal unitand the leverage assembly, when in operative engagement with the record,cooperate to provide a well balanced arrangement which is most desirablefor good performance of the pickup. Also, the manner of mounting thecrystal unit and the crank-like leverage arrangement of the vibratorymechanical system makes it possible to provide good seal betweenadjacent portions of the housing and leverage arrangment at the pointwhere said arrangement passes through the housing, since the movement atsaid point is generally rotational about an axis concentrically disposedwith respect to said portions.

In the embodiment illustrated and as can best be seen in Figure 2, thedriving chuck is of substentiall L-shaped configuration and includesacrystal-engaging portion 30 and a needle-receiving portion EH. Thecrystal-en aging portion of the driving chuck clampingly embraces thefree corner portion of the crystal unit. Suitable cement advantageouslyapplied to the contacting faces of said corner portion of the crystalunit and to said crystal-engaging portion of the driving chuck, toinsure retention of said chuck in its operative position. Theneedle-receiving portion of the driving chuck is substan ially tubularin shape, and extends from the crystal-engaging portion to pass throughopening 29 in the crystal housing. It will be noted that the opening 2:!and the chuck portion lie in an extension of the plane of the supportedcrystal unit and are located approximately midway of the length of thefree edge lid of said unit.

The needle consists of a piece of wire 32 which is conveniently securedto and projects laterally from a shank 33. This shank is substantiallycylindrical and snugly fits in the tubular portion 3! of the drivingchuck, so that the needle extends back in the direction of thecrystal-engaging portion 3:23 of said chuck. By associating the chuckand needle in this manner, the chuck and needle cooperate to form thereversely bent crank-like assembly above referred to. In order tofacilitate and to insure the desired positioning of the needle withrespect to the crystal unit and its driving chuck, a slot-and-keyarrangement is provided between said chuck and the needle shank. In thearrangement shown, a key 34 is arranged on and projects laterally fromthe needle shank for slidable engagement within slot 35 providedlongitudinally of the shank-receiving portion 3| of the driving chuck.The relative disposition of slot 35, key 34 and needle-forming wire 52,is such that the needle can assume only that position which locates itin the mentioned relationship with respect to the crystal and drivingchuck. The arrangement above described has the advantage that a damagedneedle can be readily removed for repair or replacement, Withoutdisturbing the pickup cartridge assembly.

The tubular portion 3| of the driving chuck is movably anchored inopening 29 of the housing by means of a bushing 36 of resilient materialsuch as soft rubber. This bushing seals the opening about said tubularportion and yet allows displacement of the chuck to actuate the crystalunit in response to lateral movement of the needle when trackingin't'hemodulated groove of the record. The wall defining theopeningzil-is inwardly recessed as shown at 3? in Figure 2, so toprovide an annular depression into which part of the bushing enters whensaid bushingis' pressed by clamping action of the housing sections uponbeing tightly drawn together, as by means of fastening elements 38. Inthis manner, the bushing is positively held in position, and the sealingbetween the adjacent wall surfacesof the housing and tubular portion ofthe chuck is enhanced. Furthermore, the cooperative association of thehousing wall at opening 29, of the bushing 96 and of the tubular portion3| provides the fulcrum for the operation of the leverage arrangement inthe manner above explained.

In order to establish a complete seal all around the assembled housing,the space 23 accommodating terminal strips l! and t2, the open portionof slots 2d receiving the contact pieces and 29,

and the space along the contacting edges of housing sections i8 and 59are filled, as represented at 39, with a suitable compound such assealing wax.

From the foregoing description, it will be an preciated thattheinvention provides a compact and adequately sealed crystal pickupcartridge which is of light construction suitable for use in the playingof records which require operation at exceedingly 10w needle pressure.Particularly, it Will be recognized that the arrangement which theinvention provides for the mounting and driving of the crystal unit,results in the obtainment of a piezoelectric pickup which is capable ofgood voltage output and has good response characteristics when operatingat a low needle pressure and with a fine extremely narrow modulatedgroove such as is provided on the herein mentioned improved ormicrogroove records.

I claim:

1. In a transducer for reproducing sound from a phonograph record, aflat quadrilateral piezoelectric crystal unit having corner portions,means clamping said unit along two adjacent edges so as to preventflexure of the three corner portions included in said two edges and toleave one corner portionbetween the remaining two adjacent edges free toflex, said means further supporting said unit so as to locate one ofsaid remaining two edges in substantiall confronting relation withrespect to the playing surface of a record when the transducer is inuse, and means including a driving chuck and a reproducing needle, saidchuck being connected with the free corner portion of the crystal unitto drive the same and cooperating with the needle to provide acrank-like leverage system, the pivotal axis of which is disposedgenerally in a plane perpendicular to said one confronting edge andpasses sub- 8 stantially midway between the free corner portion and theclamped corner portionof said one confronting edge.

2. A transducer as set forth in claim 1, in which the driving chuckincludes a crystal-engaging portion and a needle-receiving portion, saidcrystal-engaging portion clampingly embracing the free corner portion ofthe crystal unit, and the needle-receiving portion providing the pivotfor the crank-like leverage system.

3. A transducer as set forth in claim 2, in which the crystal-engagingportion, the needle-receiving portion and the needle received thereinare relatively disposed to constitute a reversely bent crank-likeleverage system.

4. A transducer for reproducing sound from a phonograph record,comprising in combination with a fiat four-cornered piezoelectriccrystal unit, a housing enclosing said unit and having portionscooperating to hold the crystal unit so as to prevent 'flexure of threeadjacent corners of said unit and so as to locate one edge only of theunit in substantially confronting relation with respect to the playingsurface of a record when the transducer is in use, and a leverage systemincluding a record-engaging needle and a driving chuck connected withthe fourth and free corner of said unit to drive the same, said leveragesystem being mounted in the housing for pivotal movement about an axispassing perpendicularly through said one confronting edge and lying inthe plane of said unit, the mentioned driving chuck including aneedle-receiving portion, needle-receiving portion cooperating withadjacent parts of the housing to provide the fulcrum for the leveragesystem.

5. A transducer as set forth in claim 4, in which a rubber-like bushingis pressingly engaged between the needle-receiving portion or" the chuckand adjacent parts of the housing, said bushing providing a tight sealat the fulcrum of the leverage system.

' CLEON D. ONEAL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,105,011 Williams Jan. 11, 1938'2,181,437 Norton Nov, 28, 1939 2,207,539 Gravley July 9, 1949 2,222,056Williams Nov. 19, 1940 2,286,178 Kornei June 9, 1942 2,305,369 WilliamsDec. 15, 1942 2,320,416 Dally June 1, 1943 2,363,497 Begun Nov. 28, 1944

